1. Field of the Invention
This invention relates to a method and apparatus to determine the extent and changes in the extent with time of Eustachian tube opening of a subject by measuring the phase difference and changes in the phase difference with time of sound waves applied to the nose and detected in the ear canal of a subject.
2. Description of the Prior Art
French Pat. No. 2,459,648 teaches a method for measuring Eustachian tube opening wherein a signal of determined frequency is applied at the nostril of a subject, is transmitted through the Eustachian tube during swallowing and, finally, is picked-up and measured in the ear. The patent states that the peak amplitude of the signal picked up in the ear indicates the diameter of the opening of the Eustachian tube. However, the patent further states that the signal picked up by the auricular probe is likely to be fugitive and subject to interference. Therefore, the patented method prohibits measurement of the amplitude if the signal picked up does not show a predetermined number of consecutive impulses, i.e. does not last for a predetermined time.
As the method of the French patent publication measurement of fleeting or fugitive amplitudes, it is substantially incapable of measuring rapidly changing opening sizes such as occur when the Eustachian tube diameter is changing rapidly from its fully closed state upon the onset of swallowing or from its fully open state at the end of a swallow.
There remains a need, for both clinical and research purposes, to obtain information concerning changes in the amount of Eustachian tube opening as a function of time, which involves determinations concerning the tube while its diameter is changing from its fully closed to open state and vice versa.